The following U.S. patents:
______________________________________ Patentee U.S. Pat. No. Issue Date ______________________________________ Cuneo et al. 5,085,161 February 4, 1992 Goldbach et al. 5,086,723 February 11, 1992 Goldbach et al. 5,090,351 February 25, 1992 Goldbach et al. 5,269,246 December 14, 1993 ______________________________________
disclose modular, double-walled vessel hull constructions in which one or more longitudinal walls of at least a portion of the vessel hull is fabricated of two transversally spaced longitudinal extending wall layers each made of plates weldingly joined at edges, and a series of wall layer-connecting plates, each of which has one longitudinal edge weldingly joined in a respective plate joint in one of those longitudinal wall layers, and an opposite longitudinal edge weldingly joined in the transversally corresponding plate joint in the other of those longitudinal wall layers.
A typical use of the vessel wall construction is for fabrication of modules for longitudinal midbodies of vessels for transporting flowable cargo stored in tanks each of which is defined at least in part by a layer of at least one such double walls. Some of the double walls may have a layer which forms an external boundary of the vessel, i.e., it forms part of a bottom wall or side wall of a hull. In such instances, one of the wall layers forms part of an outer hull, and the other forms part of an inner hull. In other instances, a double wall may provide a longitudinal bulkhead internally of a vessel hull, e.g., extending vertically between a bottom wall and a deck so as to divide the internal space enclosed by the hull, into a greater number of mutually isolated cargo tanks, arranged on transversally opposite sides of the longitudinal bulkhead.
Typically, in such vessel longitudinal midbody constructions, each module is a longitudinal segment of the whole, each is fabricated so as to have, not only a hull portion (including a deck portion) and possibly one or more longitudinal bulkheads, but also a transverse bulkhead, preferably provided at one end of the respective module. The modules are serially welded together end-to-end to provide a vessel longitudinal midbody. A vessel bow member is welded to one end of the longitudinal midbody, and a vessel stern member is welded to the opposite end of the longitudinal midbody, in order to constitute a complete vessel. The longitudinal bulkheads (if provided) and transverse bulkheads internally divide the space enclosed by the vessel hull into a plurality of cargo tanks. Other equipment normally provided on the particular type of vessel can be installed, as will be appreciated by those skilled in the art.
In each double wall of the vessel hull, and longitudinal bulkhead(s) (if provided), the wall layer-interconnecting plates which join the two wall layers at the plate-to-plate edge joints divide the space within each such double wall into a plurality of compartments or cells each delimited by two wall layers, two wall layer-interconnecting plates, and two transverse bulkheads.
Some of these cells can be intended to remain empty in use, or to act as pipe chaces, keel ducts, ventilation ducts or have other uses than carrying cargo. Not unusually, some can be intended for carrying (typically) sea water or river or lake water as ballast, for helping maintain a sufficiently low center of gravity and high density as to permit safe vessel operation when the cargo tanks are partly or completely empty.
In conventional double-hulled vessels, the plates which interconnect the inner and outer hulls are often provided with openings. These permit the vessel operations to fill and empty the compartments with ballast without providing piping to each compartment. They also permit the vessel operators to inspect the compartments (when the compartments are emptied of ballast), e.g., looking for corrosion damage and leaks from or to the compartments, indicating a need for repairs and maintenance. In such conventional double-hulled vessels, the openings from one compartment to the next are all aligned from plate to plate, girthwise.
This conventional layout can be the source of several problems which have safety implications.
If all the openings are provided near one end of each module, ventilation efforts will tend to be more effective at the module end that is near the openings; fumes due to leaks from the cargo tanks into the cells will tend to build towards unsafe levels at cell ends furthest from the openings while ventilation is being conducted.
Inspectors and repairers, who are climbing through the cell array, from cell to cell on ladders conventionally provided, should they slip, could fall, drop through an opening, continue to fall through the next compartment and next opening, and so on, striking ladder rings and the edges of openings, and thereby becoming seriously injured. If the ventilator or respirator that the worker is wearing is not operating properly, or has been removed by the worker, fumes that have built up at a poorly ventilated far end of a compartment could cause the worker to become dizzy, disoriented or subject to blacking out while, after walking the length of the compartment to its ventilated end, they had stepped onto the ladder to climb up or down to a neighboring compartment.
The wall layer-connecting plates in a conventional double-hulled tanker may be simple flat plates having such access openings, or they may be stiffened by stiffening ribs or plates welded or otherwise secured thereto (typically to one face, and running crosswise of the plate). A typical wall layer-connecting plate is about seven feet wide, fifty feet long, spaced about eight feet from its closest neighbors, and its access openings are two feet in diameter. The access openings may be provided with sealable hatches for selectively closing them, or they may be simple openings that are intended to remain always open. Such access openings can also be called manholes.